Cable/broadband, telecom, wireless, and satellite industries connect a variety of electrical components, e.g., antennas, amplifiers, diplexers, surge arrestors, with transmission lines, and adapters, to form systems that transmit alternating current electrical signals that can be arranged in an analog and/or digital format. One measure of the success of these systems is the efficiency with which the electrical signals are transmitted amongst these components. Engineers, designers, and technicians in these industries, however, are aware that the level of transmission efficiency that is attained is dependent, in part, on the physical properties of the components that are used in their construction.
Characteristic impedance is one of these properties. More particularly, differences in the characteristic impedance of the components that are connected together can cause problems that affect the transmission efficiency. For example, in a system that includes an antenna, an amplifier, and a transmission line, the differences in the characteristic impedance of the antenna, the amplifier, and the transmission line can cause a portion of the electrical signal transmitted from the amplifier to the antenna to reflect back to the amplifier. This, in turn, can cause standing wave patterns to form in the transmission line when the electrical signal transmitted from the amplifier to the antenna reacts with the electrical signal reflected from the antenna to the amplifier.
Impedance matching is one way to alleviate some of these problems. The goal is to create a system that has a substantially uniform characteristic impedance, which for many systems of the type disclosed and contemplated herein is nominally about 50 ohm, 75 ohm or 90 ohm. Characteristic impedance values that are exhibited by each of the transmission lines and the adapters are determined by a variety of factors, such as, for example, the geometry of the transmission line, the geometry of the adapter structure, and the corresponding dielectric material between the conductors. Similarly, it is generally recognized by those artisans having ordinary skill in the electrical arts that, in one example, the value of characteristic impedance for the adapter can be calculated according to the Equation 1 below,Z=√{square root over (Z1×Z2)},  Equation (1)where Z is the characteristic impedance of the adapter, and Z1 and Z2 are the values of characteristic impedance for various components in the system. Accordingly, creating a system having substantially uniform characteristic impedance includes matching the characteristic impedance values of the transmission lines, e.g., coaxial cable, and the adapters that electrically couple the conductors of the transmission lines with other transmission lines, and with the electrical components.
The phase of the electrical signal is another property, that can impact the transmission efficiency. More particularly, it may be necessary to shift the phase of the signal to avoid reflection of the signal in the adapter. Phase matching is therefore another way to improve the efficiency of signal transmission. This was traditionally accomplished by providing transmission lines of excess length that are assembled with a free end and a connector (or adapter) attached to the end opposite the free end of the transmission line. The excess length is purposefully left so that the transmission line can be cut to a pre-determined length on the basis of the measurement of the phase, e.g., by measuring the return loss in the system. This is a very lengthy and inefficient procedure.
To improve the phase matching process, another way to match the phase is to adjust the electrical length of the adapter, or the length of the adapter as it appears to the electrical signal. The electrical length is considered to be the length of the adapter measured in wavelengths (λ). It will be generally recognized by those artisans having ordinary skill in the electrical arts that, in one example, the electrical length can be calculated according to Equation 2 below,
                                          l            electrical                    =                                    l              f                                      984              ⁢                                                          ⁢                              V                f                                                    ,                            Equation        ⁢                                  ⁢                  (          2          )                    where lelectrical is the electrical length, lf is the length of the adapter, and Vf is the velocity factor of the adapter, e.g., the ratio of the wave velocity to the speed of light, and the numerical value 984 is provided so that the unit of measure of the electrical length (lelectrical) is provided in feet.
Changes to the electrical length of the adapter, however, can often change its value of characteristic impedance. This is not particularly preferred, of course, because it can intensify the impedance mismatch in the system, counteract the benefits that the change to the electrical length, and effectively reduce the efficiency with which the electrical signals are transmitted through the system. Adapter technology that addresses this trade off between changes in the electrical length and the need to keep constant the value of characteristic impedance has been described variously in, for example, U.S. Pat. Nos. 4,741,702 and 4,772,223 to Yasumoto, which disclose connectors where the characteristic impedance is held constant when electrical path length is adjusted, for example, by rotating portions of the connector (U.S. Pat. No. 4,741,702), or by using an adjustment element and corresponding impedance matching screws (U.S. Pat. No. 4,741,702). U.S. Pat. No. 4,724,399 to Bogar et al discloses a phase shifter where the electrical length is changed by increasing and decreasing the axial length of two opposing dielectric means. And, U.S. Pat. No. 5,746,623 to Fuchs et al. shows an integrated trimmer where the value of characteristic impedance is held constant despite changes in the electrical length. This device includes a clamping sleeve that surrounds a pair of housing parts and interior conductor parts. By turning the clamping sleeve, the housing parts translate inside of the clamping sleeve in manner that changes the electrical length of the trimmer. This arrangement, however, has several disadvantages because the housing parts translate inside of the clamping sleeve, and the conductor parts and the housings are so dimensioned so as to cause reflection points between the outer diameter of the conductor parts and the inner diameter of the housing parts.
None of the connectors discussed above, however, are configured where the physical length of the connector and the electrical length connector change, while the value of characteristic impedance remains unchanged. To some extent this may limit the applicability of the aforementioned devices, or make some particularly ill-suited to provide enough adjustment to the electrical length as is necessary to match the phase of electrical signals. For example, the proper adjustment may require that the electrical length is equal to about the wavelength (λ) of the electrical signal.
Thus, although mismatches in the characteristic impedance of the transmission lines and the adapters, as well as deviations in the phase of the electrical signal, can degrade the quality of the electronic signal, these mismatches are essentially inevitable. In fact, constraints on cost, manufacturing tolerances, and material selection, among other limitations, cause many adapters that are presently available to exacerbate the problem. Despite these issues, efforts that are directed to provide phase adjustment in combination constant characteristic impedance to balance the value of characteristic impedance of the components, transmission lines, and in particular the adapters, throughout the system have thus far been unsatisfactory, or have resulted in rigid solutions with limited application in systems utilizing higher frequency regimes.
Therefore, an adapter is needed that can facilitate phase matching without changing the nominal value of characteristic impedance of high frequency systems. It is likewise desirable that, in addition to being configured to support a range of electrical lengths, the adapter should be robust enough so that it can be implemented in a variety of systems and applications.